Introduction: Cartesian Divers

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A Cartesian Diver is a classic rising and sinking toy that uses the principles of buoyancy, density, and Boyle’s Law. Squeezing the bottle will cause the diver to sink due to the added pressure causing the air in the diver to compress. There are two versions of this toy: open and closed.

The open diver has an opening that holds a bubble of air that allows water to be pushed inside when pressure is applied on the outside of the bottle. The diver is able to float because the mass of the air within the volume of the diver gives the diver a lower density than water. When the pressure is applied this decreases the bouncy because the air is pushed into a smaller area at the top of the diver and allows for more water to enter which increases the diver’s mass even more meaning it will sink.

The closed diver is a completely closed packet that contains air, but the diver is also able to bend and compress due to the material it is made of. The diver is able to sink because the air inside the diver becomes compressed from the outside pressure. The pressure makers a smaller bubble of air inside that in turn decreases the overall volume of the diver, lowering the density, and causing the diver to sink.

Key Terms

Mass - is a measure of the amount of matter in an object

Volume - the amount of space occupied by the observed matter

Density – the degree of compactness of a substance; the quantity of mass in a given volume; Mass divided by Volume

Buoyancy – the ability or tendency to float in a fluid

Pressure – the amount of force on a until of area

Float – to rest or move on/near the surface of a fluid

Sink – to go below the surface of a fluid

Boyle’s Law – the pressure of a gas will increase as the volume decreases, if the gas is at a constant temperature.


Flexible Clear Plastic Bottle with Cap (Can be a 2-Liter, Water Bottle, Soda Bottle, Etc.)
Food Coloring* (*Optional)

Open Diver Model #1
Straight Plastic Straw Not

Open Diver Model #2
Bendy Plastic Straw


Open Diver Model #3
Pen Cap
Paperclips OR Playdoh

Closed Diver Model
Condiment Packet (Ketchup Packet, Soy Sauce Packet, etc.)

Step 1: Fill Up the Water Bottle With Water. Add Food Coloring If Desired.

Step 2: For Open Diver Model #1

Cut a section of the straw

Step 3:

Bend the straw section in half and cut a small section off the end to make the sides even with one another.

Step 4:

Add one paper clip at a time until the diver is neutrally buoyant (just floating at the top of the water).

Step 5: For Open Diver Model #2

Step 6:

Cut a section of the straw with the bend in the middle. Fold in half along the bend and cut a small section off to make the sides even.

Step 7:

Add one paper clip at a time until the diver is neutrally buoyant (just floating at the top of the water).

Step 8: Open Diver Model #3

Step 9:

Take a pen cap and tape over the top part with the hole with 3-5 layers of tape.

Step 10:

Tape ONE Paperclip to the long section of the cap,OR add a small amount of Playdoh.

Step 11:

Add one paperclip at a time OR small amounts of Playdoh until the diver is neutrally buoyant (just floating at the top of the water). You can add these onto the long part of the cap or on the cap itself. Make sure the cap is not sealed off.

Step 12: Closed Diver Model

Take the condiment packet and place it into the bottle. It should already be neutrally buoyant (just floating at the top of the water).

Step 13:

Seal the cap on the bottle VERY tight.

Step 14:

Take the bottle and squeeze hard to make the diver go down.

Further Exploration:

Vsauce D!NG – How To Make A Cartesian Diver -

NPS Physics - How Does a Submarine Sink and Rise? Soda Bottle Diver; Cartesian Diver Physics Experiment -

Science Channel – How Do Submarines Dive and Surface? -

SciShow Kids – How Do Submarines Work?